This invention relates to electronic article surveillance systems wherein the articles are provided with magnetic markers for detection of the articles and, in particular, to methods and apparatus for deactivating the magnetic markers of such systems.
Article surveillance systems are well known in the art wherein articles are provided with magnetic markers which enable the detection of unauthorized passage of the articles through an interrogation zone. In these systems, a magnetic field is established in the interrogation zone and the magnetic marker attached to an article causes a perturbation to the field when the article is in the zone. This perturbation is detected by a receiving system which activates an alarm to indicate the presence of the article.
In some systems of this type, provision is made for deactivating the marker so the article can pass through the interrogation zone without generating an alarm. Thus, for example, where passage is authorized, as where the article has been paid for, the marker would be deactivated so as to permit uninhibited passage of the article through the zone.
One way of providing the desired deactivation is to utilize in the magnetic marker adjacent strips of so-called "soft" and "hard" magnetic materials such as, for example permalloy and vicalloy, respectively. In a marker of this type, the permalloy, which has a high permeability, low coercive force and is easily saturable, would normally provide a perturbation to the field in the interrogation zone resulting in an alarm condition when an article carrying the marker passes through the zone. However, if the article is first subjected to a high magnetic field prior to reaching the interrogation zone, such as at an article check out area, this high field causes the hard material to become permanently magnetized. As a result, when the article is taken through the interrogation zone, the magnetized hard material prevents the soft material from perturbing the field in a way recognizable by the surveillance system. The article thus passes without alarming the system. Deactivating of a magnetic marker in this manner is taught, for example, in U.S. Pat. No. 3,747,086.
As above-indicated, the above-discussed deactivation procedure relies on subjecting the article carrying the marker to a high magnetic field in order to magnetize the hard magnetic material. However, use of such a high field is undesirable in applications where the articles themselves are magnetically sensitive such as, for example, magnetic tapes which are normally housed in cassettes. In such situations, the application of a high magnetic field to deactivate the marker may likely extend into the cassette and damage information on the magnetic tape.
In U.S. Pat. No. 4,665,387 there is disclosed a deactivation apparatus which attempts to avoid the necessity of having to use a high magnetic field to achieve deactivation. In this apparatus, a deactivation assembly is provided with a thin strip of hard magnetic material which is permanently magnetized along its length so that adjacent magnetized sections are of opposite magnetic polarization. The assembly is further configured so that when an article to be deactivated is brought into the assembly its magnetic marker comes to rest in close proximity to the permanently magnetized strip. This causes the hard magnetic material of the marker to become permanently magnetized with the pattern of magnetization of the strip. As a result, the soft magnetic material of the marker and, therefore, the marker itself, is rendered unable to activate its associated surveillance system.
While the apparatus of the '387 patent thus avoids the use of an uncontrolled, high deactivation field, it requires a separate deactivation assembly with its attendant expense.
Also, once the marker used with the '387 apparatus is deactivated, it must be reactivated if it is to be used again. This requires a further reactivation assembly and further added expense. Also, in the case where the article is a magnetic tape, reactivation significantly increases the risk of damaging the tape through inadvertent misuse of the reactivation assembly.
It is, therefore, a primary object of the present invention to provide a deactivation practice for a magnetic marker which avoids the need for high magnetic fields and a special deactivation assembly.
It is a further object of the present invention to provide deactivation practice which also avoids the need for a reactivation assembly.
It is yet a further object of the present invention to provide deactivation practice which can be safely used with articles carrying magnetic materials such as magnetic tape cassettes.